The present invention relates to a method and a device for driving an electronically commutated, polyphase direct current (DC) motor, whose winding strands can be connected to a DC energy source in a preestablished sequence using switching elements that are driven by an electronic commutation device, steps being provided for braking the motor running in the reverse rotation direction and for restarting it in the preferred rotation direction.
A method of this type and a device of this type are available from German Published Patent Application No. 44 19 351.
Electronically commutated DC motors, especially polyphase synchronous motors maybe used in motor vehicles, due to their small structural design, for example, as heating and/or AC blower motors. In this context, it is believed to be disadvantageous that these motors in the switched-off state can rotate in the reverse rotation direction over the fan wheels mounted on the rotor shaft. A reverse rotation direction of the motor can be brought about, for example, by impact pressure and/or air currents in the vehicle. Because the rotor of the electronically commutated synchronous motor, due to the absence of brushes, is opposed by a slight friction, which is the result exclusively of air resistance and bearing friction, a motor of this type can rotate in the reverse rotation direction up to its maximum rotational speed. If a motor of this type, rotating in the reverse rotation direction, is switched on, for example, to set a blower in operation, it is believed to be very disadvantageous that the motor, depending on the position of the rotor, starts up (moving) either in the correct rotation direction or in opposition to the desired rotation direction.
The available device and method of German Published Patent Application No. 44 19 351 provide that the voltages induced in the winding strands of the stator during the reverse rotation of the rotor are compared with a threshold value, and, in accordance with the comparison, a defined flow of current to the winding strands is brought about. In the reverse rotation direction of the motor, this defined flow of current to the winding strands is designed to bring about the controlled, active braking of the rotor. In particular, after a reverse rotation is detected by comparing the voltages induced in one preselected winding strand and in the next strand but one with the threshold value, the preselected winding strand is connected to the operational voltage by switching on a power transistor connected to this winding strand. Accordingly, a magnetic field is generated that is directed in opposition to the magnetic field of the permanent magnets rotating in the rotor, such that the reverse rotation direction of the rotor is braked. In the available method discussed above, to achieve a reliable braking action, care is taken that, during the braking, the frequency of the phase voltage amounts to half of the voltage induced in the winding strands. For this reason, the electronics must distinguish between the two rotation directions, and additional expense for component parts is necessary to make possible a reliable startup from the reverse rotation direction.
An object of an exemplary embodiment and of an exemplary method according to the present invention is to provide a method and a device for driving an electronically commutated polyphase DC motor, especially a synchronous motor, such that a motor rotating in the reverse rotation direction due to external influences is braked from its reverse rotation direction at any switch-on time and subsequently starts up in its preferred rotation direction, without any additional component units being necessary for this function, to distinguish the rotation direction of the motor.
The above objective is believed to be achieved according to an exemplary method of the present invention the present invention that has the following steps:
a first step that, in each case, selects only one phase at each time point;
a second step that carries out a commutation detection, the voltage in the selected phase induced in the corresponding motor winding being compared with a reference voltage; and
a third step that, after the commutation is detected, advances the selected phase and the phase to be commutated by the commutation device by one step in the preestablished sequence, so that, when the motor is rotating in the preferred direction, for each phase a constant current-flow angle is established, and, when the motor is rotating in the reverse direction, for each phase markedly varying current-flow angles are established, which, depending on the curve of the corresponding induced phase voltage, result in a counter-torque opposing the reverse rotation direction.
The objective is also believed to be achieved by an exemplary embodiment of a device of the present invention for driving an electronically commutated, polyphase DC motor, the device having a power switch connected to the motor, the power switch, in a preestablished sequence, supplying the individual winding strands of the motor with a pulsed DC voltage that is derived from a DC voltage source; a commutation logic driving the power switch part in accordance with the preestablished sequence; and an arrangement or structure that brakes the motor from a reverse rotation direction and sets it in motion again in the preferred rotation direction, the device having
a phase selector circuit connected to the motor windings and acted upon by an output signal from a phase discriminator circuit connected to the commutation logic, and which at every time point, selects, in each case, only one phase,
a commutation detection circuit, acted upon by the phase selected by the phase selector circuit, detects a commutation by comparing the voltage induced in the selected phase in the corresponding motor winding with a reference voltage, and generates a commutation detection signal, and
the phase discriminator circuit, and therefore the commutation logic, is advanced one step in the preestablished sequence by the commutation detection circuit in response to each commutation detection signal, so that when the motor rotates in the preferred direction, for every phase a constant current-flow angle is established, and when it rotates in the reverse direction, for every phase markedly varying current-flow angles are established, which, depending on the course of the corresponding voltage induced in each phase, generate a counter-torque opposing the reverse rotation direction.